Surgical access system and related methods

ABSTRACT

A surgical access system including a tissue distraction assembly and a tissue refraction assembly, both of which may be equipped with one or more electrodes for use in detecting the existence of (and optionally the distance and/or direction to) neural structures before, during, and after the establishment of an operative corridor to a surgical target site.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/756,951, filed on Feb. 1, 2013, which is a continuation of U.S.patent application Ser. No. 13/668,504, filed on Nov. 5, 2012, which isa continuation of U.S. patent application Ser. No. 13/030,798, filed onFeb. 18, 2011 (now U.S. Pat. No. 8,303,498), which is a continuation ofU.S. patent application Ser. No. 12/632,373 (now U.S. Pat. No.7,892,173), filed on Dec. 7, 2009, which is a division of U.S. patentapplication Ser. No. 10/789,797 (now U.S. Pat. No. 7,819,801), filed onFeb. 27, 2004, which claims priority to U.S. Provisional PatentApplications Ser. No. 60/450,806, filed Feb. 27, 2003, the entirecontents of which are hereby expressly incorporated by reference intothis disclosure as if set forth fully herein.

BACKGROUND OF THE INVENTION

I. Field of the Invention

The present invention relates generally to systems and methods forperforming surgical procedures and, more particularly, for accessing asurgical target site in order to perform surgical procedures.

II. Discussion of the Prior Art

A noteworthy trend in the medical community is the move away fromperforming surgery via traditional “open” techniques in favor ofminimally invasive or minimal access techniques. Open surgicaltechniques are generally undesirable in that they typically requirelarge incisions and high amounts of tissue displacement to gain accessto the surgical target site, which produces concomitantly high amountsof pain, lengthened hospitalization (increasing health care costs), andhigh morbidity in the patient population. Less-invasive surgicaltechniques (including so-called “minimal access” and “minimallyinvasive” techniques) are gaining favor due to the fact that theyinvolve accessing the surgical target site via incisions ofsubstantially smaller size with greatly reduced tissue displacementrequirements. This, in turn, reduces the pain, morbidity and costassociated with such procedures. The access systems developed to date,however, fail in various respects to meet all the needs of the surgeonpopulation.

One drawback associated with prior art surgical access systems relatesto the ease with which the operative corridor can be created, as well asmaintained over time, depending upon the particular surgical targetsite. For example, when accessing surgical target sites located beneathor behind musculature or other relatively strong tissue (such as, by wayof example only, the psoas muscle adjacent to the spine), it has beenfound that advancing an operative corridor-establishing instrumentdirectly through such tissues can be challenging and/or lead to unwantedor undesirable effects (such as stressing or tearing the tissues). Whilecertain efforts have been undertaken to reduce the trauma to tissuewhile creating an operative corridor, such as (by way of example only)the sequential dilation system of U.S. Pat. No. 5,792,044 to Foley etal., these attempts are nonetheless limited in their applicability basedon the relatively narrow operative corridor. More specifically, based onthe generally cylindrical nature of the so-called “working cannula,” thedegree to which instruments can be manipulated and/or angled within thecannula can be generally limited or restrictive, particularly if thesurgical target site is a relatively deep within the patient.

Efforts have been undertaken to overcome this drawback, such as shown inU.S. Pat. No. 6,524,320 to DiPoto, wherein an expandable portion isprovided at the distal end of a cannula for creating a region ofincreased cross-sectional area adjacent to the surgical target site.While this system may provide for improved instrument manipulationrelative to sequential dilation access systems (at least at deep siteswithin the patient), it is nonetheless flawed in that the deployment ofthe expandable portion may inadvertently compress or impinge uponsensitive tissues adjacent to the surgical target site. For example, inanatomical regions having neural and/or vasculature structures, such ablind expansion may cause the expandable portion to impinge upon thesesensitive tissues and cause neural and/or vasculature compromise, damageand/or pain for the patient.

This highlights yet another drawback with the prior art surgical accesssystems, namely, the challenges in establishing an operative corridorthrough or near tissue having major neural structures which, ifcontacted or impinged, may result in neural impairment for the patient.Due to the threat of contacting such neural structures, efforts thus farhave largely restricted to establishing operative corridors throughtissue having little or substantially reduced neural structures, whicheffectively limits the number of ways a given surgical target site canbe accessed. This can be seen, by way of example only, in the spinalarts, where the exiting nerve roots and neural plexus structures in thepsoas muscle have rendered a lateral or far lateral access path(so-called trans-psoas approach) to the lumbar spine virtuallyimpossible. Instead, spine surgeons are largely restricted to accessingthe spine from the posterior (to perform, among other procedures,posterior lumbar interbody fusion (PLIF)) or from the anterior (toperform, among other procedures, anterior lumbar interbody fusion(ALIF)).

Posterior-access procedures involve traversing a shorter distance withinthe patient to establish the operative corridor, albeit at the price ofoftentimes having to reduce or cut away part of the posterior bonystructures (i.e. lamina, facets, spinous process) in order to reach thetarget site (which typically comprises the disc space). Anterior-accessprocedures are relatively simple for surgeons in that they do notinvolve reducing or cutting away bony structures to reach the surgicaltarget site. However, they are nonetheless disadvantageous in that theyrequire traversing through a much greater distance within the patient toestablish the operative corridor, oftentimes requiring an additionalsurgeon to assist with moving the various internal organs out of the wayto create the operative corridor.

The present invention is directed at eliminating, or at least minimizingthe effects of, the above-identified drawbacks in the prior art.

SUMMARY OF THE INVENTION

The present invention accomplishes this goal by providing a novel accesssystem and related methods which involve detecting the existence of (andoptionally the distance and/or direction to) neural structures before,during, and after the establishment of an operative corridor through (ornear) any of a variety of tissues having such neural structures which,if contacted or impinged, may otherwise result in neural impairment forthe patient. It is expressly noted that, although described hereinlargely in terms of use in spinal surgery, the access system of thepresent invention is suitable for use in any number of additionalsurgical procedures wherein tissue having significant neural structuresmust be passed through (or near) in order to establish an operativecorridor.

According to one broad aspect of the present invention, the accesssystem comprises a tissue distraction assembly and a tissue retractionassembly, both of which may be equipped with one or more electrodes foruse in detecting the existence of (and optionally the distance and/ordirection to) neural structures. The tissue distraction assembly (inconjunction with one or more elements of the tissue retraction assembly)is capable of, as an initial step, distracting a region of tissuebetween the skin of the patient and the surgical target site. The tissueretraction assembly is capable of, as a secondary step, being introducedinto this distracted region to thereby define and establish theoperative corridor. Once established, any of a variety of surgicalinstruments, devices, or implants may be passed through and/ormanipulated within the operative corridor depending upon the givensurgical procedure. The electrode(s) are capable of, during both tissuedistraction and retraction, detecting the existence of (and optionallythe distance and/or direction to) neural structures such that theoperative corridor may be established through (or near) any of a varietyof tissues having such neural structures which, if contacted orimpinged, may otherwise result in neural impairment for the patient. Inthis fashion, the access system of the present invention may be used totraverse tissue that would ordinarily be deemed unsafe or undesirable,thereby broadening the number of manners in which a given surgicaltarget site may be accessed.

The tissue distraction assembly may include any number of componentscapable of performing the necessary distraction. By way of example only,the tissue distraction assembly may include a K-wire, an initial dilatorof split construction, and one or more dilators of traditional (that is,non-split) construction for performing the necessary tissue distractionto receive the remainder of the tissue retractor assembly thereafter.One or more electrodes may be provided on one or more of the K-wire anddilator(s) to detect the presence of (and optionally the distance and/ordirection to) neural structures during tissue distraction.

The tissue retraction assembly may include any number of componentscapable of performing the necessary retraction. By way of example only,the tissue retraction assembly may include one or more retractor bladesextending from a handle assembly. The handle assembly may be manipulatedto open the retractor assembly; that is, allowing the retractor bladesto separate from one another simultaneously to create an operativecorridor to the surgical target site. In a preferred embodiment, this isaccomplished by maintaining a posterior retractor blade in a fixedposition relative to the surgical target site (so as to avoid having itimpinge upon any exiting nerve roots near the posterior elements of thespine) while the additional retractor blades (i.e. cephalad-most andcaudal-most blades) are moved or otherwise translated away from theposterior retractor blade (and each other) so as to create the operativecorridor in a fashion that doesn't infringe upon the region of theexiting nerve roots.

The retractor blades may be optionally dimensioned to receive and directa rigid shim element to augment the structural stability of theretractor blades and thereby ensure the operative corridor, onceestablished, will not decrease or become more restricted, such as mayresult if distal ends of the retractor blades were permitted to “slide”or otherwise move in response to the force exerted by the displacedtissue. In a preferred embodiment, only the posterior retractor blade isequipped with such a rigid shim element. In an optional aspect, thisshim element may be advanced into the disc space after the posteriorretractor blade is positioned, but before the retractor is opened intothe fully retracted position. The rigid shim element is preferablyoriented within the disc space such that is distracts the adjacentvertebral bodies, which serves to restore disc height. It alsopreferably advances a sufficient distance within the disc space(preferably past the midline), which serves the dual purpose ofpreventing post-operative scoliosis and forming a protective barrier(preventing the migration of tissue (such as nerve roots) into theoperative field and the inadvertent advancement of instruments outsidethe operative field).

The retractor blades may optionally be equipped with a mechanism fortransporting or emitting light at or near the surgical target site toaid the surgeon's ability to visualize the surgical target site,instruments and/or implants during the given surgical procedure.According to one embodiment, this mechanism may comprise, but need notbe limited to, providing one or more strands of fiber optic cable withinthe walls of the retractor blades such that the terminal (distal) endsare capable of emitting light at or near the surgical target site.According to another embodiment, this mechanism may comprise, but neednot be limited to, constructing the retractor blades of suitablematerial (such as clear polycarbonate) and configuration such that lightmay be transmitted generally distally through the walls of the retractorblade light to shine light at or near the surgical target site. This maybe performed by providing the retractor blades having light-transmissioncharacteristics (such as with clear polycarbonate construction) andtransmitting the light almost entirely within the walls of the retractorblade (such as by frosting or otherwise rendering opaque portions of theexterior and/or interior) until it exits a portion along the interior(or medially-facing) surface of the retractor blade to shine at or nearthe surgical target site. The exit portion may be optimally configuredsuch that the light is directed towards the approximate center of thesurgical target site and may be provided along the entire innerperiphery of the retractor blade or one or more portions therealong.

BRIEF DESCRIPTION OF THE DRAWINGS

Many advantages of the present invention will be apparent to thoseskilled in the art with a reading of this specification in conjunctionwith the attached drawings, wherein like reference numerals are appliedto like elements and wherein:

FIG. 1 is a perspective view of a tissue retraction assembly (in use)forming part of a surgical access system according to the presentinvention;

FIG. 2 is a perspective view illustrating the components and use of aninitial distraction assembly (i.e. K-wire, an initial dilating cannulawith handle, and a split-dilator housed within the initial dilatingcannula) forming part of the surgical access system according to thepresent invention, for use in distracting to a surgical target site(i.e. annulus);

FIG. 3 is a perspective view illustrating the K-wire and split-dilatorof the initial distraction assembly with the initial dilating cannulaand handle removed;

FIG. 4 is a posterior view of the vertebral target site illustrating thesplit-dilator of the present invention in use distracting in a generallycephalad-caudal fashion according to one aspect of the presentinvention;

FIG. 5 is a side view illustrating the use of a secondary distractionassembly (comprising a plurality of dilating cannulae over the K-wire)to further distract tissue between the skin of the patient and thesurgical target site according to the present invention;

FIGS. 6-7 are perspective and side views, respectively, of a retractorassembly according to the present invention, comprising a handleassembly having three (3) retractor blades extending there from(posterior, cephalad-most, and caudal-most) disposed over the secondarydistraction assembly of FIG. 5 (shown in a first, closed position);

FIGS. 8-10 are perspective, side and top views, respectively, of theretractor assembly of FIGS. 6-7 in a second, opened (i.e. retracted)position (over the secondary distraction assembly) to thereby create anoperative corridor to a surgical target site according to the presentinvention;

FIGS. 11-13 are perspective, side and top views, respectively, of theretractor assembly of FIGS. 6-7 in the second, opened (i.e. refracted)position (with the secondary distraction assembly removed) illustratingthe operative corridor to the surgical target site according to thepresent invention;

FIG. 14 is an enlarged perspective view of the interior surface of aretractor blade, illustrating a pair of dove-tail grooves dimensioned toengage a shim element (as shown in FIG. 15) and/or a retractor extender(as shown in FIG. 16) according to the present invention;

FIG. 15 is a perspective view of a shim element dimensioned to beadjustably and removably coupled to a retractor blade (as shown in FIG.14) according to the present invention;

FIG. 16 is a perspective view of a retractor extender dimensioned to beadjustably and removably coupled to a retractor blade (as shown in FIG.14) according to the present invention;

FIGS. 17-18 are perspective and side views, respectively, of theretractor assembly illustrating the use of an introducer device forcoupling the shim element of FIG. 15 to the posterior retractor bladeand introducing the distal end of the shim (shim extension) into theintradiscal space according to the present invention;

FIGS. 19-21 are perspective, side and top views, respectively, of theretractor assembly illustrating the shim element after introductionaccording to the present invention;

FIG. 22 is a side view of the retractor assembly illustrating the shimelement and one of two retractor extenders after introduction accordingto the present invention;

FIG. 23 is a perspective view of an exemplary nerve monitoring systemcapable of performing nerve monitoring before, during and after thecreating of an operative corridor to a surgical target site using thesurgical access system in accordance with the present invention;

FIG. 24 is a block diagram of the nerve monitoring system shown in FIG.23; and

FIGS. 25-26 are screen displays illustrating exemplary features andinformation communicated to a user during the use of the nervemonitoring system of FIG. 23.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Illustrative embodiments of the invention are described below. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. It will of course be appreciated thatin the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure. It is furthermore to be readily understood that,although discussed below primarily within the context of spinal surgery,the surgical access system of the present invention may be employed inany number of anatomical settings to provide access to any number ofdifferent surgical target sites throughout the body. The surgical accesssystem disclosed herein boasts a variety of inventive features andcomponents that warrant patent protection, both individually and incombination.

The present invention involves accessing a surgical target site in afashion less invasive than traditional “open” surgeries and doing so ina manner that provides access in spite of the neural structures requiredto be passed through (or near) in order to establish an operativecorridor to the surgical target site. Generally speaking, the surgicalaccess system of the present invention accomplishes this by providing atissue distraction assembly and a tissue retraction assembly, both ofwhich may be equipped with one or more electrodes for use in detectingthe existence of (and optionally the distance and/or direction to)neural structures.

These electrodes are preferably provided for use with a nervesurveillance system such as, by way of example, the type shown anddescribed in co-pending and commonly assigned Int'l Patent ApplicationSer. No. filed Sep. 25, 2002 (claiming priority to U.S. Provisional App.Ser. No. 60/325,424 filed on Sep. 25, 2001), the entire contents ofwhich are expressly incorporated by reference as if set forth herein intheir entirety (“the '424 PCT”). Generally speaking, this nervesurveillance system is capable of detecting the existence of (andoptionally the distance and/or direction to) neural structures duringthe distraction and retraction of tissue by detecting the presence ofnerves by applying a stimulation signal to such instruments andmonitoring the evoked EMG signals from the myotomes associated with thenerves being passed by the distraction and retraction systems of thepresent invention. In so doing, the system as a whole (including thesurgical access system of the present invention) may be used to form anoperative corridor through (or near) any of a variety of tissues havingsuch neural structures, particularly those which, if contacted orimpinged, may otherwise result in neural impairment for the patient. Inthis fashion, the access system of the present invention may be used totraverse tissue that would ordinarily be deemed unsafe or undesirable,thereby broadening the number of manners in which a given surgicaltarget site may be accessed.

The tissue distraction assembly of the present invention (comprising aK-wire, an initial dilator, and a split-dilator disposed within theinitial dilator) is employed to distract the tissues extending betweenthe skin of the patient and a given surgical target site (preferablyalong the posterior region of the target intervertebral disc). Asecondary distraction assembly (i.e. a plurality of sequentiallydilating cannulae) may optionally be employed after the initialdistraction assembly to further distract the tissue. Once distracted,the resulting void or distracted region within the patient is ofsufficient size to accommodate a tissue retraction assembly of thepresent invention. More specifically, the tissue retraction assembly(comprising a plurality of retractor blades extending from a handleassembly) may be advanced relative to the secondary distraction assemblysuch that the retractor blades, in a first, closed position, areadvanced over the exterior of the secondary distraction assembly. Atthat point, the handle assembly may be operated to move the retractorblades into a second, open or “retracted” position to create anoperative corridor to the surgical target site.

According to one aspect of the invention, following (or before) thisretraction, a posterior shim element (which is preferably slideablyengaged with the posterior retractor blade) may be advanced such that adistal shim extension in positioned within the posterior region of thedisc space. If done before retraction, this helps ensure that theposterior retractor blade will not move posteriorly during theretraction process, even though the other retractor blades (i.e.cephalad-most and caudal-most) are able to move and thereby create anoperative corridor. Fixing the posterior retractor blade in this fashionserves several important functions. First, the distal end of the shimelement serves to distract the adjacent vertebral bodies, therebyrestoring disc height. It also rigidly couples the posterior retractorblade in fixed relation relative to the vertebral bodies. The posteriorshim element also helps ensure that surgical instruments employed withinthe operative corridor are incapable of being advanced outside theoperative corridor, preventing inadvertent contact with the exitingnerve roots during the surgery. Once in the appropriate retracted state,the cephalad-most and caudal-most retractor blades may be locked inposition and, thereafter, retractor extenders advanced therealong toprevent the ingress or egress of instruments or biological structures(i.e. nerves, vasculature, etc. . . . ) into or out of the operativecorridor. Once the operative corridor is established, any of a varietyof surgical instruments, devices, or implants may be passed throughand/or manipulated within the operative corridor depending upon thegiven surgical procedure.

FIG. 1 illustrates a tissue retraction assembly 10 forming part of asurgical access system according to the present invention. Theretraction assembly 10 includes a plurality of retractor bladesextending from a handle assembly 20. By way of example only, the handleassembly 20 is provided with a posterior retractor blade 12, acephalad-most retractor blade 16, and a caudal-most retractor blade 18.Although shown and described below with regard to the three-bladedconfiguration, it is to be readily appreciated that the number ofretractor blades may be increased or decreased without departing fromthe scope of the present invention. The retractor assembly 10 is shownin a fully retracted or “open” configuration, with the retractor blades12, 16, 18 positioned a distance from one another so as to form anoperative corridor 15 there between and extending to a surgical targetsite (i.e. an annulus of an intervertebral disc).

The retractor blades 12, 16, 18 may be equipped with various additionalfeatures or components. By way of example only, posterior retractorblade 12 may be equipped with a shim element 22 (shown more clearly inFIG. 15). Shim element 22 serves to distract the adjacent vertebralbodies (thereby restoring disc height), helps secure the retractorassembly 10 relative to the surgical target site, and forms a protectivebarrier to prevent the ingress or egress of instruments or biologicalstructures (i.e. nerves, vasculature, etc. . . . ) into or out of theoperative corridor. Each of the remaining retractor blades(cephalad-most blade 16 and caudal-most blade 18) may be equipped with aretractor extender 24 (shown more clearly in FIG. 16). The retractorextenders 24 extend from the cephalad-most and caudal-most refractorblades 16, 18 to form a protective barrier to prevent the ingress oregress of instruments or biological structures (i.e. nerves,vasculature, etc. . . . ) into or out of the operative corridor.

According to the present invention, any or all of the retractor blades12, 16, 18, the shim element 22 and/or the retractor extender 24 may beprovided with one or more electrodes 39 (preferably at their distalregions) equipped for use with a nerve surveillance system, such as, byway of example, the type shown and described in the NeuroVision PCTApplications set forth below.

The handle assembly 20 may be coupled to any number of mechanisms forrigidly registering the handle assembly 20 in fixed relation to theoperative site, such as through the use of an articulating arm mountedto the operating table. The handle assembly 20 includes first and secondarm members 26, 28 hingedly coupled via coupling mechanism 30 (i.e.bolt/nut combination disposed through receiving apertures formed alongarm members 26, 28). The cephalad-most retractor blade 16 is rigidlycoupled (generally perpendicularly) to the end of the first arm member26. The caudal-most retractor blade 18 is rigidly coupled (generallyperpendicularly) to the end of the second arm member 28. With combinedreference to FIG. 10, the posterior retractor blade 12 is rigidlycoupled (generally perpendicularly to) a translating member 17, which iscoupled to the handle assembly 20 via a linkage assembly 14. The linkageassembly 14 includes a first link 34 hingedly disposed between thetranslating member 17 and a point along the first arm member 26 of thehandle assembly 20, and a second link 36 hingedly disposed between thetranslating member 17 and the second arm member 28 of the handleassembly 20. The translating member 17 includes a translation slot 19through the bolt/nut combination of the coupling mechanism 30 mayengage. In use, a user can squeeze the proximal ends of the arms 26, 28and thereby cause the coupling mechanism 30 to translate distally withinthe slot 19, which increases the relative distance between the posteriorretractor blade 12 and the cephalad-most and caudal-most refractorblades 16, 18. This squeezing motion of the arms 26, 28 simultaneouslycauses the cephalad-most and caudal-most retractor blades 16, 18 to moveaway from one another. Taken collectively, the diameter of the operativecorridor 15 increases at approximately the same time. An optionallocking mechanism 35 (i.e. bolt and nut combination extending betweenarm members 26, 28) may be provided to selectively lock the arm members26, 28 relative to one another to thus maintain the retractor assembly10 in the fully retracted position, once achieved.

FIG. 2 illustrates an initial distraction assembly 40 forming part ofthe surgical access system according to the present invention. Theinitial distraction assembly 40 includes a K-wire 42, an initialdilating cannula 44 with handle 46, and a split-dilator 48 housed withinthe initial dilating cannula 44. In use, the K-wire 42 and split-dilator48 are disposed within the initial dilating cannula 44 and the entireassembly 40 advanced through the tissue towards the surgical target site(i.e. annulus). Again, this is preferably accomplished while employingthe nerve detection and/or direction features described above. After theinitial dilating assembly 40 is advanced such that the distal ends ofthe split-dilator 48 and initial dilator 44 are positioned within thedisc space (FIG. 2), the initial dilator 44 and handle 46 are removed(FIG. 3) to thereby leave the split-dilator 48 and K-wire 42 in place.As shown in FIG. 4, the split-dilator 48 is thereafter split such thatthe respective halves 48 a, 48 b are separated from one another todistract tissue in a generally cephalad-caudal fashion relative to thetarget site. The split dilator 48 may thereafter be relaxed (allowingthe dilator halves 48 a, 48 b to come together) and rotated such thatthe dilator halves 48 a, 48 b are disposed in the anterior-posteriorplane. Once rotated in this manner, the dilator halves 48 a, 48 b areagain separated to distract tissue in a generally anterior-posteriorfashion. Each dilator halve 48 a, 48 b may be, according to the presentinvention, provided with one or more electrodes (preferably at theirdistal regions) equipped for use with a nerve surveillance system, suchas, by way of example, the type shown and described in the NeuroVisionPCT Applications set forth below.

Following this initial distraction, a secondary distraction may beoptionally undertaken, such as via a sequential dilation system 50 asshown in FIG. 5. According to the present invention, the sequentialdilation system 50 may include the K-wire 42, the initial dilator 44,and one or more supplemental dilators 52, 54 for the purpose of furtherdilating the tissue down to the surgical target site. Once again, eachcomponent of the secondary distraction assembly 50 (namely, the K-wire42, the initial dilator 44, and the supplemental dilators 52, 54 may be,according to the present invention, provided with one or more electrodes(preferably at their distal regions) equipped for use with a nervesurveillance system, such as, by way of example, the type shown anddescribed in the NeuroVision PCT Applications set forth below.

As shown in FIGS. 6-7, the retraction assembly 10 of the presentinvention is thereafter advanced along the exterior of the sequentialdilation system 50. This is accomplished by maintaining the retractorblades 12, 16, 18 in a first, closed position (with the retractor blades12-16 in generally abutting relation to one another). Once advanced tothe surgical target site, the handle assembly 20 may be operated asshown in FIGS. 8-10 to move the retractor blades 12, 16, 18 into asecond, open or “retracted” position. As one can see, the posteriorretractor blade 12 is allowed to stay in the same general positionduring this process, such that the cephalad-most and caudal-mostretractor blades 14, 16 move away from the posterior retractor blade 12.Again, this is accomplished through the cooperation between thetranslation member 17 (attached to the posterior refractor blade 12) andthe arms 26, 28 of the handle assembly 20 via the linkage assembly 14and slot 19 in conjunction with the coupling mechanism 30. FIGS. 11-13illustrate the retractor assembly 10 in the second, opened (i.e.retracted) position (with the secondary distraction assembly 50 removedfor clarity) illustrating the operative corridor 15 to the surgicaltarget site according to the present invention.

FIGS. 14-16 illustrate an important aspect of the present invention,wherein (FIG. 15) each retractor blade 12, 16, 18 is provided with apair of engagement grooves 37 having, by way of example only, agenerally dove-tailed cross-sectional shape. The engagement grooves 37are dimensioned to engage with dove-tail elements 41 provided on theshim element 22 (FIG. 15) and each retractor extender 24 (FIG. 16). In apreferred embodiment, the shim element 22 and retractor extender 24 areeach provided with an elongate slot 43 and tool-engaging elements 45. Atool may be used to bias the arms 47 of each device inwardly towards oneanother (decreasing the width of part or most of the slot 43), whichforces the dove-tail elements 41 towards one another. This is shown, byway of example only, in FIGS. 17-18, wherein a tool 59 is used tointroduce the shim element 22 into engaged relation with the posteriorretractor blade 12. When the shim element 22 has been introduced to adesired position (such as having the distal end extend into theintradiscal space as best shown in FIGS. 18 and 20), the tool 59 maythen be disengaged or released from the tool-engaging elements 45 suchthat the dove-tail elements 41 return to their normal position (beingbiased outwardly by the resiliency of the arms 47) to thereby secure theshim element 22 relative to the posterior retractor blade 12. FIGS.19-21 illustrate the shim element 22 after introduction according to thepresent invention. The same process can be used with the retractorextender 24 shown in FIG. 16 with respect to the cephalad-most andcaudal-most refractor blades 16, 18. The end result is shown in FIG. 22with the retraction assembly 10 of the present invention disposed inposition over a surgical target site.

Nerve Surveillance

According to yet another aspect of the present invention, any number ofdistraction components and/or retraction components (including but notlimited to those described herein) may be equipped to detect thepresence of (and optionally the distance and/or direction to) neuralstructures during the steps tissue distraction and/or retraction. Thisis accomplished by employing the following steps: (1) one or morestimulation electrodes are provided on the various distraction and/orretraction components; (2) a stimulation source (e.g. voltage orcurrent) is coupled to the stimulation electrodes; (3) a stimulationsignal is emitted from the stimulation electrodes as the variouscomponents are advanced towards or maintained at or near the surgicaltarget site; and (4) the patient is monitored to determine if thestimulation signal causes muscles associated with nerves or neuralstructures within the tissue to innervate. If the nerves innervate, thismay indicate that neural structures may be in close proximity to thedistraction and/or refraction components.

Neural monitoring may be accomplished via any number of suitablefashions, including but not limited to observing visual twitches inmuscle groups associated with the neural structures likely to found inthe tissue, as well as any number of monitoring systems, including butnot limited to any commercially available “traditional” electromyography(EMG) system (that is, typically operated by a neurophysiologist. Suchmonitoring may also be carried out via the surgeon-driven EMG monitoringsystem shown and described in the following commonly owned andco-pending PCT Applications (collectively “NeuroVision PCTApplications”): PCT App. Ser. No. PCT/US02/22247, entitled “System andMethods for Determining Nerve Proximity, Direction, and Pathology DuringSurgery,” filed on Jul. 11, 2002; PCT App. Ser. No. PCT/US02/30617,entitled “System and Methods for Performing Surgical Procedures andAssessments,” filed on Sep. 25, 2002; PCT App. Ser. No. PCT/US02/35047,entitled “System and Methods for Performing Percutaneous PedicleIntegrity Assessments,” filed on Oct. 30, 2002; and PCT App. Ser. No.PCT/US03/02056, entitled “System and Methods for Determining NerveDirection to a Surgical Instrument,” filed Jan. 15, 2003. The entirecontents of each of the above-enumerated NeuroVision PCT Applications ishereby expressly incorporated by reference into this disclosure as ifset forth fully herein.

In any case (visual monitoring, traditional EMG and/or surgeon-drivenEMG monitoring), the access system of the present invention mayadvantageously be used to traverse tissue that would ordinarily bedeemed unsafe or undesirable, thereby broadening the number of mannersin which a given surgical target site may be accessed.

FIGS. 23-24 illustrate, by way of example only, a monitoring system 120of the type disclosed in the NeuroVision PCT Applications suitable foruse with the surgical access system 10 of the present invention. Themonitoring system 120 includes a control unit 122, a patient module 124,and an EMG harness 126 and return electrode 128 coupled to the patientmodule 124, and a cable 132 for establishing electrical communicationbetween the patient module 124 and the surgical access system 10 (FIG.1). More specifically, this electrical communication can be achieved byproviding, by way of example only, a hand-held stimulation controller152 capable of selectively providing a stimulation signal (due to theoperation of manually operated buttons on the hand-held stimulationcontroller 152) to one or more connectors 156 a, 156 b, 156 c. Theconnectors 156 a, 156 b, 156 c are suitable to establish electricalcommunication between the hand-held stimulation controller 152 and (byway of example only) the stimulation electrodes on the K-wire 42, thedilators 44, 52, 54, the retractor blades 12, 16, 18 and/or the shimelements 22, 24 (collectively “surgical access instruments”).

In order to use the monitoring system 120, then, these surgical accessinstruments must be connected to the connectors 156 a, 156 b and/or 156c, at which point the user may selectively initiate a stimulation signal(preferably, a current signal) from the control unit 122 to a particularsurgical access instruments. Stimulating the electrode(s) on thesesurgical access instruments before, during and/or after establishingoperative corridor will cause nerves that come into close or relativeproximity to the surgical access instruments to depolarize, producing aresponse in a myotome associated with the innervated nerve.

The control unit 122 includes a touch screen display 140 and a base 142,which collectively contain the essential processing capabilities(software and/or hardware) for controlling the monitoring system 120.The control unit 122 may include an audio unit 118 that emits soundsaccording to a location of a surgical element with respect to a nerve.The patient module 124 is connected to the control unit 122 via a datacable 144, which establishes the electrical connections andcommunications (digital and/or analog) between the control unit 122 andpatient module 124. The main functions of the control unit 122 includereceiving user commands via the touch screen display 140, activatingstimulation electrodes on the surgical access instruments, processingsignal data according to defined algorithms, displaying receivedparameters and processed data, and monitoring system status and reportfault conditions. The touch screen display 140 is preferably equippedwith a graphical user interface (GUI) capable of communicatinginformation to the user and receiving instructions from the user. Thedisplay 140 and/or base 142 may contain patient module interfacecircuitry (hardware and/or software) that commands the stimulationsources, receives digitized signals and other information from thepatient module 124, processes the EMG responses to extractcharacteristic information for each muscle group, and displays theprocessed data to the operator via the display 140.

In one embodiment, the monitoring system 120 is capable of determiningnerve direction relative to one or more of the surgical accessinstruments before, during and/or following the creation of an operativecorridor to a surgical target site. Monitoring system 120 accomplishesthis by having the control unit 122 and patient module 124 cooperate tosend electrical stimulation signals to one or more of the stimulationelectrodes provided on these instruments. Depending upon the location ofthe surgical access system 10 within a patient (and more particularly,to any neural structures), the stimulation signals may cause nervesadjacent to or in the general proximity of the surgical access system 10to depolarize. This causes muscle groups to innervate and generate EMGresponses, which can be sensed via the EMG harness 126. The nervedirection feature of the system 120 is based on assessing the evokedresponse of the various muscle myotomes monitored by the system 120 viathe EMG harness 126.

By monitoring the myotomes associated with the nerves (via the EMGharness 126 and recording electrode 127) and assessing the resulting EMGresponses (via the control unit 122), the surgical access system 10 iscapable of detecting the presence of (and optionally the distant and/ordirection to) such nerves. This provides the ability to activelynegotiate around or past such nerves to safely and reproducibly form theoperative corridor to a particular surgical target site, as well asmonitor to ensure that no neural structures migrate into contact withthe surgical access system 10 after the operative corridor has beenestablished. In spinal surgery, for example, this is particularlyadvantageous in that the surgical access system 10 may be particularlysuited for establishing an operative corridor to an intervertebraltarget site in a postero-lateral, trans-psoas fashion so as to avoid thebony posterior elements of the spinal column.

FIGS. 25-26 are exemplary screen displays (to be shown on the display140) illustrating one embodiment of the nerve direction feature of themonitoring system shown and described with reference to FIGS. 23-24.These screen displays are intended to communicate a variety ofinformation to the surgeon in an easy-to-interpret fashion. Thisinformation may include, but is not necessarily limited to, a display ofthe function 180 (in this case “DIRECTION”), a graphical representationof a patient 181, the myotome levels being monitored 182, the nerve orgroup associated with a displayed myotome 183, the name of theinstrument being used 184 (in this case, a dilator 46, 48), the size ofthe instrument being used 185, the stimulation threshold current 186, agraphical representation of the instrument being used 187 (in this case,a cross-sectional view of a dilator 46, 48) to provide a reference pointfrom which to illustrate relative direction of the instrument to thenerve, the stimulation current being applied to the stimulationelectrodes 188, instructions for the user 189 (in this case, “ADVANCE”and/or “HOLD”), and (in FIG. 15) an arrow 190 indicating the directionfrom the instrument to a nerve. This information may be communicated inany number of suitable fashions, including but not limited to the use ofvisual indicia (such as alpha-numeric characters, light-emittingelements, and/or graphics) and audio communications (such as a speakerelement). Although shown with specific reference to a dilating cannula(such as at 184), it is to be readily appreciated that the presentinvention is deemed to include providing similar information on thedisplay 140 during the use of any or all of the various instrumentsforming the surgical access system 10 of the present invention,including the distraction assemblies 40, 50, the retractor blades 12,16, 18 and/or the shim members 22, 24.

The surgical access system 10 of the present invention may be sold ordistributed to end users in any number of suitable kits or packages(sterile and/or non-sterile) containing some or all of the variouscomponents described herein.

As evident from the above discussion and drawings, the present inventionaccomplishes the goal of gaining access a surgical target site in afashion less invasive than traditional “open” surgeries and, moreover,does so in a manner that provides the ability to access such a surgicaltarget site regardless of the neural structures required to be passedthrough (or near) in order to establish an operative corridor to thesurgical target site. The present invention furthermore provides theability to perform neural monitoring in the tissue or regions adjacentthe surgical target site during any procedures performed after theoperative corridor has been established. The surgical access system ofthe present invention can be used in any of a wide variety of surgicalor medical applications, above and beyond the spinal applicationsdiscussed herein. Such spinal applications may include any procedurewherein instruments, devices, implants and/or compounds are to beintroduced into or adjacent the surgical target site, including but notlimited to discectomy, fusion (including PLIF, ALIF, TLIF and any fusioneffectuated via a lateral or far-lateral approach and involving, by wayof example, the introduction of bone products (such as allograft orautograft) and/or devices having ceramic, metal and/or plasticconstruction (such as mesh) and/or compounds such as bone morphogenicprotein), total disc replacement, etc. . . . ).

Moreover, the surgical access system of the present invention opens thepossibility of accessing an increased number of surgical target sites ina “less invasive” fashion by eliminating or greatly reducing the threatof contacting nerves or neural structures while establishing anoperative corridor through or near tissues containing such nerves orneural structures. In so doing, the surgical access system of thepresent invention represents a significant advancement capable ofimproving patient care (via reduced pain due to “less-invasive” accessand reduced or eliminated risk of neural contact before, during, andafter the establishment of the operative corridor) and lowering healthcare costs (via reduced hospitalization based on “less-invasive” accessand increased number of suitable surgical target sites based on neuralmonitoring). Collectively, these translate into major improvements tothe overall standard of care available to the patient population, bothdomestically and overseas.

While certain embodiments have been described, it will be appreciated bythose skilled in the art that variations may be accomplished in view ofthese teachings without deviating from the spirit or scope of thepresent application. For example, with regard to the monitoring system120, it may be implemented using any combination of computer programmingsoftware, firmware or hardware. As a preparatory act to practicing thesystem 120 or constructing an apparatus according to the application,the computer programming code (whether software or firmware) accordingto the application will typically be stored in one or more machinereadable storage mediums such as fixed (hard) drives, diskettes, opticaldisks, magnetic tape, semiconductor memories such as ROMs, PROMs, etc.,thereby making an article of manufacture in accordance with theapplication. The article of manufacture containing the computerprogramming code may be used by either executing the code directly fromthe storage device, by copying the code from the storage device intoanother storage device such as a hard disk, RAM, etc. or by transmittingthe code on a network for remote execution. As can be envisioned by oneof skill in the art, many different combinations of the above may beused and accordingly the present application is not limited by the scopeof the appended claims.

What is claimed is:
 1. A system for accessing a surgical target site,the system comprising: a three-bladed tissue retraction assemblycomprising: a first retractor arm having a first length extendingbetween a first proximal end and a first distal end, the first retractorarm comprising a first blade connecting portion at the first distal endand a first pivot portion toward the first proximal end; a secondretractor arm having a second length extending between a second proximalend and a second distal end, the second retractor arm comprising asecond blade connecting portion at the second distal end and a secondpivot portion toward the second proximal end; a coupling mechanismhingedly connecting the first pivot portion of the first retractor armand the second pivot portion of the second retractor arm such that thefirst retractor arm is pivotable with respect to the second retractorarm about the coupling mechanism; a translating member defining atranslation slot extending along a length of the translating member andhaving a third blade connecting portion at a distal end of thetranslating member, wherein the first and second retractor arms areslidably connected to the translating member at the translation slot viathe coupling mechanism; a caudal-most retractor blade connected to thefirst blade connecting portion of the first retractor arm at a proximalend of the caudal-most retractor blade; a cephalad-most retractor bladeconnected to the second blade connecting portion of the second retractorarm at a proximal end of the cephalad-most retractor blade, whereinpivoting the first retractor arm with respect to the second retractorarm moves the caudal-most retractor blade away from the cephalad-mostretractor blade; and a posterior-most retractor blade connected to thethird blade connecting portion of the translating member at a proximalend of the posterior-most retractor blade, wherein sliding the couplingmechanism in the translation slot toward the distal end of thetranslation member causes the caudal-most retractor blade and thecephalad-most retractor blade to translate in unison away from theposterior-most retractor blade.
 2. The system of claim 1, wherein thetissue retraction assembly further comprises: a shim mechanicallyengagable with the posterior-most retractor blade so as to be positionedon an inner side of the posterior-most retractor blade and extend past adistal end of the posterior-most retractor blade.
 3. The system of claim2, wherein one of the shim and the posterior-most retractor blade definefirst and second engagement grooves dimensioned to engage with first andsecond edges of the other of the shim and the posterior-most retractorblade.
 4. The system of claim 2, wherein the shim comprises a shimproximal end and a shim distal end with a proximal section near theproximal end, a distal section near the distal end, and a middle sectionbetween the proximal section and the distal section, wherein theproximal section is wider than the middle section which is wider thanthe distal section, and wherein the shim defines an elongate slotextending from a proximal edge at the shim proximal end toward thedistal end.
 5. The system of claim 1, wherein each of the retractorblades curve inward toward a working corridor defined between theretractor blades, wherein the retractor blades are actuable between aclosed position with each of the retractor blades adjacent each of theother of the retractor blades to define a substantially closed workingcorridor and a retracted position with each of the retractor bladesspaced from each of the other of the retractor blades to define an openworking corridor.
 6. The system of claim 1, wherein the tissueretraction assembly further comprises: a shim mechanically engagablewith the posterior-most retractor blade so as to extend past a distalend of the posterior-most retractor blade; a first retractor extendermechanically engagable with the caudal-most retractor blade so as toextend past a distal end of the caudal-most retractor blade; and asecond retractor extender mechanically engagable with the cephalad-mostretractor blade so as to extend past a distal end of the cephalad-mostretractor blade, wherein the shim extends further in a distal directionthan each of the first and second retractor extenders and wherein theshim is narrower at its distal end than the first and second retractorextenders.
 7. The system of claim 6, wherein each of the caudal-mostretractor blade, cephalad-most retractor blade, posterior-most retractorblade, shim, first retractor extender, and second retractor extender hasat least one stimulation electrode at distal regions thereof.
 8. Thesystem of claim 1, and further comprising: a sequential dilation systemcomprising a plurality of dilators sized for the tissue retractionassembly to be advanced over the sequential dilation system, whereineach of the plurality of dilators has at least one stimulation electrodeat distal regions of the plurality of dilators, and wherein each of thecaudal-most retractor blade, cephalad-most retractor blade, andposterior-most retractor blade has at least one stimulation electrode atdistal regions of the caudal-most retractor blade, cephalad-mostretractor blade, and posterior-most retractor blade; and a nervesurveillance system electrically connectable to each of the dilators andretractor blades and configured to stimulate the dilators and retractorblades when inserted into tissue proximate nerves.
 9. The system ofclaim 8, wherein the nerve surveillance system comprises: an EMG(electromyography) harness having a plurality of recording electrodespositioned along branches of the EMG harness in pairs, wherein eachbranch of the EMG harness has a plurality of pairs of recordingelectrodes; and a control unit operably connectable to the stimulationelectrodes to activate the stimulation electrodes and to the recordingelectrodes on the EMG harness to receive EMG response signals from therecording electrodes.
 10. The system of claim 1, wherein at least two ofthe retractor blades comprise light-transmission paths extending throughthe retractor blades between inner and outer walls of the retractorblades and toward light exiting portions on the inner walls of theretractor blades.
 11. The system of claim 1, wherein the first retractorarm has a first handle extension portion extending between the firstproximal end and the first pivot portion and wherein the secondretractor arm has a second handle extension portion extending betweenthe second proximal end and the second pivot portion.
 12. The system ofclaim 1, wherein the three-bladed retraction assembly is configured tomaintain a trans-psoas operative corridor to the surgical target site ata lumbar spine, the system further comprising means for trans-psoasdilation to define a tissue distraction corridor.
 13. The system ofclaim 12, wherein the means for trans-psoas dilation comprises asequential dilation system configured to advance through a psoas muscleto define the tissue distraction corridor.
 14. The system of claim 13,wherein the sequential dilation system comprises a plurality of dilatorssized for the tissue retraction assembly to be advanced over thesequential dilation system.
 15. The system of claim 12, wherein themeans for trans-psoas dilatation defines an outer cylindrical surfacesized to slidingly mate with curved inwardly facing surfaces of thecaudal-most retactor blade, the cephalad-most retractor blade, and theposterior-most retractor blade.
 16. The system of claim 12, wherein themeans for trans-psoas dilatation comprises at least one stimulationelectrode at a distal region so as to output electrical stimulationwithin a psoas muscle.
 17. The system of claim 16, further comprisingmeans for nerve monitoring during the output of the electricalstimulation within the psoas muscle.
 18. The system of claim 17, whereinthe means for nerve monitoring comprises a nerve surveillance systemelectrically connectable to said at least one stimulation electrode ofthe each of the means for trans-psoas dilatation.
 19. The system ofclaim 17, wherein the means for nerve monitoring comprises: a sensorharness having a plurality of recording electrodes positioned alongbranches of the sensor harness in pairs, wherein each branch of thesensor harness has a plurality of pairs of recording electrodes; and acontrol unit operably connectable to said at least one stimulationelectrode and to the recording electrodes on the sensor harness toreceive neuromuscular response signals from the recording electrodes.20. A system for accessing a surgical target site, the systemcomprising: a three-bladed tissue retraction assembly comprising: afirst retractor arm having a first length extending between a firstproximal end and a first distal end, the first retractor arm comprisinga first blade connecting portion at the first distal end and a firstpivot portion toward the first proximal end; a second retractor armhaving a second length extending between a second proximal end and asecond distal end, the second retractor arm comprising a second bladeconnecting portion at the second distal end and a second pivot portiontoward the second proximal end; a coupling mechanism hingedly connectingthe first pivot portion of the first retractor arm and the second pivotportion of the second retractor arm such that the first retractor arm ispivotable with respect to the second retractor arm about the couplingmechanism; a translating member defining a translation slot extendingalong a length of the translating member and having a third bladeconnecting portion at a distal end of the translating member, whereinthe first and second retractor arms are slidably connected to thetranslating member at the translation slot via the coupling mechanism; afirst retractor blade connected to the first blade connecting portion ofthe first retractor arm at a proximal end of the first retractor blade;a second retractor blade connected to the second blade connectingportion of the second retractor arm at a proximal end of the secondretractor blade, wherein pivoting the first retractor arm with respectto the second retractor arm moves the first retractor blade away fromthe second retractor blade; a third retractor blade connected to thethird blade connecting portion of the translating member at a proximalend of the third retractor blade, wherein sliding the coupling mechanismin the translation slot toward the distal end of the translation membercauses the first retractor blade and the second retractor blade totranslate in unison away from the third retractor blade wherein at leasttwo of the retractor blades comprise light-transmission paths extendingthrough the retractor blades between inner and outer walls of theretractor blades and toward light exiting portions on the inner walls ofthe retractor blades; and a shim mechanically engagable with the thirdretractor blade so as to be positioned on an inner side of the thirdretractor blade and extend past a distal end of the third retractorblade, wherein one of the shim and the third retractor blade definefirst and second engagement grooves dimensioned to engage with first andsecond edges of the other of the shim and the third retractor blade,wherein the shim comprises a shim proximal end and a shim distal endwith a proximal section near the proximal end, a distal section near thedistal end, and a middle section between the proximal section and thedistal section, wherein the proximal section is wider than the middlesection which is wider than the distal section, and wherein the shimdefines an elongate slot extending from a proximal edge at the shimproximal end toward the distal end; a first retractor extendermechanically engagable with the first retractor blade so as to extendpast a distal end of the first retractor blade; and a second retractorextender mechanically engagable with the second retractor blade so as toextend past a distal end of the second retractor blade, wherein the shimextends further in a distal direction than each of the first and secondretractor extenders and wherein the shim is narrower at its distal endthan the first and second retractor extenders; a sequential dilationsystem comprising: a plurality of dilators sized for the tissueretraction assembly to be advanced over the sequential dilation system,wherein each of the plurality of dilators has at least one stimulationelectrode at distal regions of the plurality of dilators, and whereineach of the first retractor blade, second retractor blade, and thirdretractor blade has at least one stimulation electrode at distal regionsof the first retractor blade, second retractor blade, and thirdretractor blade; and a nerve surveillance system electricallyconnectable to each of the dilators and retractor blades and configuredto stimulate the electrodes on the dilators and retractor blades wheninserted into tissue proximate nerves, wherein the nerve surveillancesystem comprises: an EMG (electromyography) harness having a pluralityof recording electrodes positioned along branches of the EMG harness inpairs, wherein each branch of the EMG harness has a plurality of pairsof recording electrodes; and a control unit operably connectable to thestimulation electrodes to activate the stimulation electrodes and to therecording electrodes on the EMG harness to receive EMG response signalsfrom the recording electrodes.